Your business finance course has motivated you to begin investing for retirement in your company's 401K plan. Your first $500 monthly investment will be made one month from today and you plan to retire 40 years from today. How much more will you have to invest each month, if you wait for 15 years before starting to invest to end up with the same amount of money at retirement? Assume a rate of return of 0.75 percent per month for your investments.